On Sun, 31 Dec 2006, Muli Ben-Yehuda wrote:
> On Sun, Dec 31, 2006 at 02:32:25PM -0500, Robert P. J. Day wrote:
>
> > Generally, inline functions are preferable to macros resembling
> > functions.
>
> This should be stressed, IMHO. We have too many macros which have no
> reason to live.
>
> > -Macros with multiple statements should be enclosed in a do - while block:
> > +There are two techniques for defining macros that contain multiple
> > +statements.
> >
> > -#define macrofun(a, b, c) \
> > - do { \
> > + (a) Enclose those statements in a do - while block:
> > +
> > + #define macrofun(a, b, c) \
> > + do { \
> > + if (a == 5) \
> > + do_this(b, c); \
> > + } while (0)
> > +
> > + (b) Use the gcc extension that a compound statement enclosed in
> > + parentheses represents an expression:
> > +
> > + #define macrofun(a, b, c) ({ \
> > if (a == 5) \
> > do_this(b, c); \
> > - } while (0)
> > + })
>
> When giving two alternatives, the reader will thank you if you
> explain when each should be used. In this case, the second form
> should be used when the macro needs to return a value (and you can't
> use an inline function for whatever reason), whereas the first form
> should be used at all other times.
that's a fair point, although it's certainly not the coding style
that's in play now. for example,
#define setcc(cc) ({ \
partial_status &= ~(SW_C0|SW_C1|SW_C2|SW_C3); \
partial_status |= (cc) & (SW_C0|SW_C1|SW_C2|SW_C3); })
there would appear to be *lots* of cases where the ({ }) notation is
used when nothing is being returned. i'm not sure you can be that
adamant about that distinction at this point.
rday
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